1. Field of the Invention
The present invention relates to an actuator for an ink jet printer head. In particular, the invention relates an actuator for an ink jet printer head using a shape memory alloy and an insulating film.
2. Description of the Prior Art
FIGS. 1a through 1f show a conventional manufacturing method of actuator for ink jet printer head using a shape memory alloy.
Photoresist 12 is coated on silicon substrate 10 to form a pattern after which it is etched. Part removed by etching is covered with polysilicon 14 and a shape memory alloy layer 16 is formed in wished pattern upon silicon substrate 10.
Polysilicon 14 is removed by etching after the shape memory alloy layer 16 formation; and the shape memory alloy layer 16 becomes a cantilever structure by bending deformation as in FIG. 1f after polysilicon 14 removal.
FIGS. 2a through 2d show the usual manufacturing method of an actuator for ink jet printer head using a shape memory alloy.
Silicon substrate 20 is used for a substrate plate in the actuator for an ink jet printer head using a shape memory alloy.
Insulating film 22 is formed upon silicon substrate 20 upon which film then the shape memory alloy layer 24 is formed.
After shape memory alloy layer 24 has been formed, lower space part is formed by etching the silicon substrate 20 below. Whence insulating film 22 plays the etching interruption layer role.
Bending deformation takes place at insulation film 22 by stress after etching. Then bending deformation takes place also at shape memory alloy layer 24 according to the above bending deformation of insulation film 22.
Actuator for ink jet printer head using a shape memory alloy manufactured by method described above generally consists of silicon substrate 20 where lower space is formed, insulation film 22 formed to cover lower space part upon silicon substrate 20, and shape memory alloy layer 24 formed upon the insulation film 22.
FIG. 3 shows actuator for ink jet printer head using a shape memory alloy, manufactured by method as shown in FIGS. 2a through 2d; and FIG. 4 shows the jet unit part of ink jet printer head applying the actuator.
As shown in FIG. 4, chamber 26 and nozzle 28 are formed upon actuator using a shape memory alloy as in FIG. 3.
If actuator is electrified, shape memory alloy layer 24 of actuator recovers flat state which is mother shape, according to which shape transformation the volume of chamber 26 formed upon shape memory alloy layer 24 is decreased, whereby ink in chamber 26 is jetted through nozzle 28 to execute printing.
In traditional actuator for ink jet printer head using a shape memory alloy as above, initial transformation of shape memory alloy layer is controlled using compressive stress of silicon oxide film as only silicon oxide film is used for insulation film.
There it is difficult to control compressive stress deformation direction and size and also there is problem that fatigue phenomenon arises by repetitive use.
Purpose of the present invention to solve the above problem is to provide actuator for ink jet printer head using a shape memory alloy, optimized of ink ejection characteristics by shape memory effect of shape memory alloy, by controlling the internal stress by way of material and thickness of insulation film which transforms in multilayer construction with shape memory alloy.
The invention to achieve the above purpose features an actuator for ink jet printer head using a shape memory alloy, the actuator comprising: a lower space part; a silicon substrate where the lower space part is formed; an insulating film formed on the silicon substrate surface and made of silicon nitride film which acts to pull the shape memory alloy film in a direction opposite to nozzle side; and a shape memory alloy layer formed on the insulation film so as to cover the lower space part, whereby initial transformation direction and magnitude are controlled.
And the invention features an actuator for ink jet printer head using a shape memory alloy, the actuator comprising: a lower space part; a silicon substrate where the lower space part is formed; an insulating film formed on the silicon substrate surface and made of a silicon oxide film which acts to push the shape memory alloy film to nozzle side direction and a silicon nitride film which acts to pull the shape memory alloy film in a direction opposite to nozzle side; and a shape memory alloy layer formed on the insulation film so as to cover the lower space part, whereby initial transformation direction and magnitude are controlled.